The present invention relates in general to internal combustion engines, particularly four-stroke motor-vehicle engines with five cylinders in line, each including a crankshaft with crank pins which are equi-angularly spaced around the axis of the shaft and provided with balancing counterweights.
In engines of this type, there is a problem in balancing the resultant moments of the centrifugal forces of the rotating masses and the rotary components of the first-order alternating forces.
Balancing systems are known for this purpose which have counterweights designed so that each has a static moment opposed to that of the respective crank pin. This solution, however, involves the use of very large counterweights which are sometimes incompatible with the space available for the installation of the engine in the vehicle. In fact, in order to balance the said moments, which are indicated M.sub.c below, it is necessary for the counterweights to achieve a static moment m.sub.s given by the formula: EQU M.sub.c =a.multidot.i.multidot.m.sub.s .multidot..omega..sup.2
where a is a coefficient which depends on the engine type (for example a=0.449 for a five-cylinder, in-line engine), and i is the interaxial spacing of the cylinders.
m.sub.s is therefore large since a and i are small.